//
you're reading...

Ecology

Penguins can rock their bodies without eating high trophic level prey

Morrison, K.,  Bury, S., Thompson, D., (2014).  Higher trophic level prey does not represent a higher quality diet in a threatened seabird: implications for relating population dynamics to diet shifts inferred from stable isotopes.  Marine Biology.  161:2243–2255.  DOI: 10.1007/s00227-014-2502-y

A rockhopper penguin tends to its chick (Photo Credit: Paddy Gallagher - Flickr Creative Commons)

A rockhopper penguin tends to its chick (Photo Credit: Paddy Gallagher – Flickr Creative Commons)

Figuring out an optimal diet for ourselves is a lifelong affair, and for animals that have to hunt, it’s even harder! Wild animals can’t just help themselves to a pantry full of energy and nutrient dense prey, they have to factor in the abundance and ease of catch as well. The best wild diet maximizes the energy gained, net of expenditures in the shortest amount of time. An eastern rockhopper penguin’s (Eudyptes chrysocome filholi) menu consists of zooplankton such as krill, as well as cephalopods and fish. And since fish, a higher trophic level prey, are more energy dense than zooplankton or cephalopods, and more easily digested, they are scientifically considered higher quality prey.

Formally, the largest population of eastern rockhopper penguins, a subspecies of southern rockhopper penguins could be found on Campbell Island in New Zealand. However, between 1942 and 1984, the population drastically crashed by around 94% from an estimated 800,000 breeding pairs to 51,500. Breeding penguins fast for long periods of time as they take turns incubating and guarding their eggs and hatchlings, so having a higher body weight often means higher reproductive success.

Some scientists posited that nutritional stress resulting from a shift in the availability of prey from a higher trophic level prey to a lower one, due to warmer sea surface temperatures caused the significant decline.

Morrison et al., wanted to investigate if penguins consuming higher trophic level prey such as fish and cephalopods actually achieve a better body condition as inferred by body weight. In order to do so, samples of blood from 70 chicks, 55 adult females and 55 adult males of eastern rockhopper penguins were obtained over three years (2010-2012) at Penguin Bay, Campbell Island between October and January. Body weight was measured using a spring scale and blood samples were taken using a needle and syringe and stored in ethanol. The samples were then processed for stable isotope analysis (SIA) during which nitrogen and carbon were analyzed. Nitrogen isotopes evaluate the trophic level of prey. Fish and cephalopods have higher 15N:14N ratio, or δ15N when compared with zooplankton. If the blood sample yields a high δ15N, this means a larger proportion of the penguin’s diet consists of higher trophic level prey. Carbon isotopes can identify the environment of prey. Plankton closer to shore have a higher 13C:12C ratio, or δ13C, compared to further, pelagic plankton. If a blood sample yields a high δ13C, then the penguin is favouring prey closer to shore. Results of the samples were then compared with body mass in order to tease out what exactly is a high quality diet for eastern rockhoppers.

Body mass in grams of (a) adult female and (b) adult male eastern rockhopper penguins in 2011 (white) and 2012 (black) at arrival to colony (circles) and after foraging trips (triangles) plotted against 15N. The line in b reveals the negative relationship.

Turns out, higher trophic level prey does not translate to heavier chicks. δ15N and δ13C values were not related to chick body mass. Older chicks (24 days after hatching) were even heavier in 2011 when fed lower trophic prey compared to 2012. As for adults, there was not a significant relationship between body mass at arrival to the colony to δ15N (See figure on left). However, Female δ13C values were positively correlated with body mass meaning females were foraging for prey closer to the colony site before breeding. While there was no correlation between body mass and δ15N values in females during incubation forages, the results for male rockhoppers were surprising. Contrary to expectations, males with lower δ15N and δ13C values were heavier, meaning successful males actually consumed lower trophic level zooplankton near the nest area!

Shifting to a lower trophic level prey will not necessarily result in nutritional stress and population decline. This result should stand as a precaution for assuming this in other species. Shifting to a lower trophic level diet may actually represent a higher quality diet if more abundant. These surprising results inspire an alternative hypothesis; that rockhopper penguins are more likely to thrive when zooplankton prey is plentiful. Rockhoppers are increasingly competing against commercial fisheries for their prey. Breeding penguins are of greater concern since they fast for long periods of time and are even more susceptible to a decline in local prey since they are colony-based when hatching and rearing their chicks.  This brings to light urgent conservation implications, especially since they are considered vulnerable to extinction under IUCN.  Insight into an optimal diet for these goofy looking critters, can ultimately be used to keep them around.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 9 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com